The present invention relates to a control valve. More particularly, the present invention relates to a dual poppet fluid control valve, which includes a combined inlet and sensing poppet and an anti-tiedown device that prevents the control valve from operating, if the control valve reset has been tied down.
Machine tools of various types operate through a valving system, which interacts with a pneumatic, controlled clutch and/or brake assembly. For safety reasons, the control valves that are used to operate these machine tools require the operator to actuate two separate control signal applying contacts essentially simultaneously. This requirement of simultaneous application ensures that the operator will not have his hand near the moving components of the machine tool when an operating cycle is initiated. The two-control signal applying contacts can then be connected to the valving system that allows compressed air to be delivered to the machine tool to perform its operating cycle.
Safety rules and regulations require the valving system to be designed such that if a component in the valving system malfunctions, the valving system will not allow additional movement of the machine tool. In addition, the valving system must ensure that a new operation cycle of the machine tool cannot be initiated after a component of the valving system has become defective.
Prior art electromagnetic valving systems which are utilized for the operation of machine tools meet these safety requirements through the use of a double valve assembly. The double valve assembly, includes two electromagnetic supply valves which are normally closed. Each of the supply valves is moved to an open position in response to an electrical control signal. The two supply valves are arranged in series with respect to the source of compressed air. The double valve assembly also includes two exhaust valves, which are normally open. Each exhaust valve is closed by a respective supply valve when it is opened. It is therefore necessary for the supply valves to be opened simultaneously otherwise, supply air will be exhausted from the system through one of the exhaust valves. The opening and closing of the valve units is monitored by sensing air pressures in the respective valve units and then comparing these two pressures. The monitoring and comparing of these two pressures is accomplished by using a single air cylinder that is separated into two chambers by a piston. The pressure in each valve unit is delivered to one of the chambers. Thus, unequal pressures in the valve units will cause movement of the normally static piston, which will then interrupt the electrical signal to one of the valve units. This and other external electronic monitoring arrangements are expensive and require that electrical signal processing equipment be designed and utilized.
The continued development of the valving systems for machine tools has been directed toward more reliable, simpler and less costly valving systems which both meet and exceed the safety performance requirements in force today as well as those proposed for the future.
The present invention provides the art with a control valve system having a housing defining an inlet, an outlet and an exhaust. A first passage extends between the inlet and the outlet and a second passage extends between the outlet and the exhaust. A first plurality of valves are disposed within the first passage, wherein each of the first plurality of valves are movable between a deactuated position where the first passage is closed, an actuated position where the first passage is open, and an intermediate position where the first passage is partially open. A second plurality of valves are disposed within the second passage, wherein each of the second plurality of valves are movable between a deactuated position where the second passage is open, an actuated position where the second passage is closed, and an intermediate position where the second passage is partially open. A plurality of reset members are selectively engageable with the first plurality of valves. The plurality of reset members are operable to move the first plurality of valves to the deactuated position when a pressure is applied to the plurality of reset members. The plurality of reset members each have an anti-tiedown stem extending therefrom to prevent operation of the control valve system if any of the plurality of reset members is tied down.
The above-described invention clearly meets the requirement that valving systems for more reliable, simpler, and less costly valving systems which both meet and exceed the safety performance requirements in force today as well as those proposed for the future. In some such systems, however, operators sometimes attempt to maintain the reset in an operating position in order to attempt to prevent the machine from locking out in response to a malfunction.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.